Alloy



Patented Feb. 9, 1943 anam- ALLOY Louis Henri Francois Canac and Emile Auguste Marie Antoine Segol, Toulon, Var, France, as-

Alliages Autoproteges,

Paris (Seine), France, a society of France signors to Socit N Drawing.

7 Claims.

Our invention relates to light and ultra-light alloys containing aluminium and magnesium. More particularly it relates to aluminium-magnesium base alloys and a method of making the same whereby certain desirable properties insuch alloys are assured. This application is a continuation-in-part of our application Serial No. 279,992, which is itself a continuation-in-part of our application Serial No. 150,880, filed June 28, 1937.

The principal object of the invention resides in the provision of a self-protecting film on the surface of the alloy which guards the alloy from corrosion in sea water and the like. This fihn has the remarkabl capacity of cicatrizing. That is, if the film is fractured or broken, this fracture is immediately closed up or healed" by the-automatic formation of a protective scar.

Ordinary aluminium-magnesium base alloys heretofore known do not possess this remarkable property. While some of the literature has given examples of aluminium-magnesium base alloys whch are resistant to corrosion, no example has been disclosed of an alloy having a self-healing protective film, and no discharge, of which we are aware, has in any way taught how an alloy having such a remarkable property can be produced particularly with any degree of assurance.

The invention is based on a remarkable discovery we have made after many experiments and is based on a new principle.

According to this new principle and discovery, an alloy is formed of aluminium and magnesium, and by utilizing predetermined proportions of these base metals, and by adding other metals which meet very rigid'requirements as to amounts and properties, there is automatically formed on the surface of the alloy a uniform, adherent, leakproof, protective film which possesses the astounding property of cicatrizing (forming a scar, healing, closing up) immediately after fracture.

It is consequently the principal object of our.

dictates of the following specification are fol-' lowed.

Application May 13, 1940, Serial In France July 11, 1936 A more specific object of the iiivention is the provision of an alloy having a self-protectiveand critical low percentage for magnesium.

when certain requisites of the invention are carried out, results in the formation of a multitude of galvanic couples. These galvanic couples, being finely distributed, assure the rapid formation of the protective film in the presence of a normally corrosive agent such as sea water.

As already indicated the results desired can only be obtained by rigidly observing certain requisites. Particularly these requisites will now be described.

The alloy has a base of aluminium and magnesium. These base metals should be employed only in an extremely pure state. Impurities should be avoided and in any case should be less than 0.10%. This is particularly so of iron and silicon whose presence is exceptionally undesirable and even fatal to the results desired.

When the base of the alloy is such that aluminium predominates, then the proportion of stances be less than 10%. This percentage is the The many experiments carried out inmaking the invention demonstrated that the important results magnesium used is 10% or greater. The results eiiected by the invention are increasingly manifest when the proportion of magnesium is greater than 10%.

Moreover, these results are obtained with proportions of magnesium greater than The invention thus extends to the so called ultralight alloys in which magnesium predominates.

The lower and upper limits for aluminium are respectively 1% and I An alloy containing only aluminium and magnesium even with the proportions given above will not give the results of the present invention. In addition to these metals, in the proportions set forth, We have found that the invention can only be carried out by carefully selecting and adding at least two additional metals in accordance with specific requirements. v

The additional metals must first of all be easily oxidizable.

. l Secondly, the additional metals should be more precious than the base metals. Any other metal not responding to these conditions should be excluded as an impurity inconsistent with the object desired.

The oxidizing property of the addition metals acts primarily in the electrolytic formation of unattackable oxides or oxychlorides, which make up the protective self-healing film. This, however, is only produced by galvanic couples formed between the addition metals and the base metals and in which the ionsare displaced from the particles of the addition metals by the base metal. Hence, the requirement that the addition metals should be more precious than the base metals aluminium and magnesium.

When mention is made herein of metals which are more precious than the base metals, reference is had to' the electromotive series which lists the metals with respect to their activity, that is, the ease with which they give up electrons. In general, as is well known, each metal displaces the ions of those which follow it in the list.

Another requirement of the addition metals is that they must be capable of forming a eutectic with at least one of the base metals and should be present in an amount which preferably will approximate the amount which will form a eutectic with the base metals. This contributes to assure a fine distribution of the metals and gives rise to a great number of elementary piles between which electrolytic action is exerted to a maximum when the alloy is exposed to the action of a corrosive agent such as salt water.

The term eutectic is a definite term known to those skilled in metallurgy. The kind of metals and the amounts thereof which will form a eutectic with another metal can, of course, be determined from phase diagrams in the technical literature.

When we say that the addition metals should be capable of forming a eutectic mixture with at least one of the basic constituents aluminium and magnesium, and that such addition metals should be present inan amount approximating the amount required to form a eutectic mixture, we intend to cover slight variations. We have found that if the addition metal is present in amounts within 30 to +30 of the eutectic amount satisfactory results can be obtained.

Any metals which do not meet these requirements are to be excluded, .and insofar as this. invention is concerned such other metals should be regarded as impurities.

which the amounts of the addition metals are the approximate values of the proportion corresponding to the eutectic of the binary diagram of aluminium and the addition metals:

Per cent Antimony -4 1.1 Chromium 0.40 0.7'7 Cobalt 1 Beryllium 0.90 Manganese 1.95 Titanium 0.15 Cadmium 5 As an example, we may have an alloy meeting the requirements of the invention and which consists of Per cent Magnesium l0 Zirconium .2 Titanium 1 Aluminium The remainder A preferred example using titanium is as follows:

An alloy of the composition just recited showed very good results when subjected to the action of a corrosive agent. After alternate immersion While there are several metals which meet the requirements for the addition metal given above and which'can be used in accordance with theinvention, we prefer zirconium as one of the addition metals, the other addition metal or metals being taken for instance among the following: antimony, chromium, cobalt, beryllium, manganese, titanium, cadmium, nickel, boron, bismuth, molybdenum.

- 6 Insofar aszirconium is concerned this should be added in amounts ranging from 0.05 to 0.2%, preferably 0.18%, to obtain the best results although amounts up to 2% may be used with the desired results. The lower and upper limits for zirconium are respectively'0.01% and 3%.

As for other addition metals, it is preferable, but not necessary, to add them in proportions approximating those corresponding to the eutectic points formed by these addition metals with the base metals. These proportions are well knownto those skilled in the art, and as has been indicated, can be obtained from phase diagrams in the technical iiterature.-

-' For' example, the following table is given in and emersion at thirty minute intervals in sea 'water for two months, no appreciable corrosion was observed. Another sample of the same alloy showed no appreciable signs of corrosion after two months continuous immersion.

In all instances the surface of the alloy at the end of the period was covered with protective film. It was found that the protective selfhealing film formed more rapidly where the immersion was continuous.

Mechanical properties of the alloy were found to be particularly good when the alloy is rolled. A breaking strength of .45 kg. and an elongation of the order 17% were obtained. These results are further improved in alloys according to the invention where the proportion of magnesium is about 10.5%. i

The titanium may be replaced by other metals provided the conditions referred to above are 0 are observed:

' Percent Ni. 5 Cd 5 Use may also be made of the following as the fourth metal, in proportions preferably less than 1%: 4

Boron Bismuth Molybdenum We have found that alloys produced according to the invention may be further improved by heat treatment, notably tempering. This heat treatment is designed also to improve the fineness of precipitation of the crystals formed by the addition metals as well as the so called beta crystals ,8 (AlsMgz).

The temperature and duration of the heat treatment depend both on the percentage of additions and the magnesium content of the alloy;

The tempering is not carried to as great a degree where the alloy has a high magnesium content, but, in each case, the duration and temperature thereof have an optimum value. It is particularly important that the duration and temperature should not be carried to coalescence of the precipitated granules.

By way of example, considering an alloy with magnesium 11.5% and zirconium 0.18%, here is the heat treatment which should preferably be applied: In the case of the alloy being in the raw state in which it is after pouring, its resistance to corrosion is materially improved by being heated to a temperature ranging from 320 to 410 C.

In the case of an alloy to be rolled, the rolling operation is preferably carried out after anneal-- C., and cooling.

The heat treatment for giving resistance to corrosion is then carried out at a temperature ranging from 245 to 320 0., preferably close to this last mentioned value. If it is advisable to effect a supplementary rolling operation, a new treatment is carried out at a temperature of 400 or more. In a general manner, for the alloys with which the invention is concerned the tempering should be used if the ingot or rolled plates have been very rapidly cooled. The desired structure of the alloy may also be obtained directly by suitable slow cooling .of the ingot or of the sheets during the rolling, for example, by

stopping for about fifteen minutes starting from a temperature generally above 300 0., in which the granules can precipitate.

We'claim:

1. A corrosion resistive alloy having a surface formed of a multitude of galvanic couples which surface when subjected to corrosive influences is capable of forming a self-protective, cicatrizing,

film, said alloy consisting of magnesium in an amount ranging from to 50%, zirconium in an amount ranging from .05 to 2% and titanium in the amount of 1%, the balance being aluminium.

2. A corrosion resistive alloy having a surface formed of a multitude of galvanic couples which surface when subjected to corrosive influences is capable of forming a'self-protective, cicatrizing, film, said alloy consisting of magnesium in an amount ranging from 10% to 15%, zirconium in an amount ranging from .02% to 2% and titanium in the amount of 0.20, the balance being aluminium.

' 3. A corrosion resistive alloy having a surface formed of a multitude of galvanic couples which surface when subjected to corrosive influences is capable of forming a self-protective, cicatrizing, film, said alloy consisting of magnesium in the amount of 10.5%, zirconium in the amount ranging from '.08% to .11%, and titanium in the amount of .08%, and the :balance being aluminium, said alloy containing less than 0.1% of impurities, all metals being considered as impurities which are not easily oxidized, are less precious than aluminium or magnesium and which are incapable of forming a eutectic with aluminium or magnesium.

4. A corrosion resistive alloy having a surface formed of a multitude of galvanic couples which surface when subjected to corrosive influences is capable of forming a self-protective, cicatrizing, film, said alloy consisting of magnesium in the amount of 10.5%, zirconium in the amount of .11%, titanium in the amount of .08%, and the balance being aluminium, said alloy containing less than 0.1% of impurities, all metals being considered as impurities which are not easily oxidized,.are less precious than aluminium or magnesium and which are incapable of forming a eutectic with aluminium or magnesium.

5. A corrosion resistive alloy having a surface formed of a multitude of galvanic couples which surface when subjected to corrosive influences is capable of forming a self-protective, cicatrizing, film, said alloy consisting of a magnesium in an amount ranging from 10 to zirconium in an amount ranging from .02 to 2%, and titanium in an amount ranging from .08 to 1%, the balance being aluminum.

6. A corrosion resistive alloy having a surface formed of a multitude of galvanic couples which surface when subjected to corrosive influences is capable of forming a self-protective, cicatrizing film, said alloy consisting of magnesium in an amount ranging from 10 to 15%, zirconium in an amount ranging from .01 to 3%, and titanium in an amount ranging from .08 to 1%, the balance being substantially all aluminum.

7. A corrosion resistive alloy having a surface formed of a multitude of galvanic couples which surface when subjected to corrosive influences is capable of forming a self-protective, cicatrizing film, said alloy consisting of magnesium in an amount ranging from 10 to 50%, zirconium in an amount ranging from .01 to 3%, and titanium in an amount ranging from .08 to 1%, the balance being substantially all aluminum.

LOUIS HENRI FRANCOIS CANAC.

EMILE AUGUSTE MARIE ANTOINE SEGOL. 

